The present invention relates generally to the reception of MPEG-2 data, and more specifically to the framing of MPEG-2 Data.
The international organization for standards (ISO) moving pictures experts group (MPEG group), approved an audio video digital compression standard known as MPEG-2 in an effort to provide a versatile compression standard capable of being utilized for a wide variety of data. The MPEG-2 standard provides explanations needed to implement an MPEG-2 decoder through the use of syntax and semantics of a coded bit stream. MPEG-2 is an open standard which continues to evolve and be applied to a variety of applications ranging from video conferencing to high definition television. As a generic standard, MPEG-2 is intended to be used for variety of audio and video coding applications. Part one of the MPEG-2 standard (ISO 13818-1), was designated to improve error resilience and carry multiple programs simultaneously without a common time base between programs.
The transport stream (TS) specified by the MPEG-2 standard, offers a high degree of robustness for noisy channels, and can be used to carry multiple programs, such as multiple TV services. The transport stream is based on a 188 byte long packet suited for hardware error correction and processing schemes. The use of a robust protocol, such as the transport stream, allows for reception over noisy environments such as terrestrial and satellite transmissions. Even in these environments it is possible to obtain fast program access, channel hopping, and synchronization between multiple elementary streams carried within the packetized elementary streams which are subdivided into transport packets.
Prior art FIG. 1 illustrates a Transport Packet Stream defined by the MPEG-2 standard. The transport stream, based on a 188 byte long packet, is well suited for hardware error correction and processing schemes. Such a configuration can carry multiple programs within the same multiplex, even when the transmission environment is noisy. For example, MPEG-2 data can be transferred successfully over coaxial cable networks and satellite transponders with asynchronous multiplexing of constant or variable bit-rate programs to allow fast program access, channel hoping and synchronization between services.
As illustrated further in FIG. 1, MPEG-2 transport stream consists of fixed length Transport Stream Packets (TSP or packets) based on 4 bytes of header followed by 184 bytes of TSP payload. TSP payload carries Packetized Elementary Stream (PES) data obtained by chopping up an Elementary Stream (ES), which consists of data of a common type and program. For example, audio for a specific program would form one elementary stream, while video for the same program would form a second elementary stream.
The TS header consists of a synchronization byte (SyncByte), flags, information indicators for error detection and timing, an adaptation field indicator, and a Packet_ID (PID) field used to identify Elementary Streams carried in the payload. The adaptation field, when present, contains flags, and timing information.
The PID Field is used not only to distinguish separate Elementary Streams, but also separate Program Specific Information (PSI) tables. Prior art FIG. 2 illustrates two types of PSI tablesxe2x80x94a Program Association Table 210 (PAT), and a Program Map Table 220 (PMT). The PAT table lists unique program numbers as identifiers for each program, or elementary stream, in a multiplex, and the PID number associated with each program number. A fixed PID number of 0x0000 is assigned to the PAT table, making it possible for the system to download the PAT table on startup by retrieving PID 0x0000 packets.
Each program identified the PAT table has a related Program Map Table (PMT) having its own PID identifier. Each PMT table lists the PIDs for all Elementary Streams (components) making a given program associated with the PMT. A specific PMT table maybe constructed for each program separately, or may be common for a group of programs. In the first case, there are many PMT tables with just one section, and each PMT table has a different PID value. In the second case one PMT table may have many sections, each relevant to one program.
In order to provide multiple services over the same multiplex, data associated with different multimedia services are transmitted, with packet multiplexing, such that data packets from several Elementary Streams of audio, video, data, and others are interleaved on a packet by packet basis into a single MPEG-2 transport stream. Synchronization between Elementary Streams forming a common program is achieved using presentation time stamps and program clock references which can be transmitted as part of the adaptation field specified in the header.
Prior art FIG. 3 illustrates the fields associated with a PES stream. Each PES stream contains a header portion and a data portion. In addition, an optional header portion may exist. The header portion includes a Packet Start Prefix, a stream ID, and a packet length indicator.
Transport stream information can be provided either through a direct broadcast, or through a service provider broadcast. Direct broadcast generally refers to signals which are received directly by an end user. Examples of direct broadcasts include satellite broadcasts received by satellite dishes and provided to a decoder at the end user""s location, which receives and decodes the transport stream data. Another type of direct broadcast is the traditional composite television/radio broadcast. In their most elementary forms, these broadcasts are not digital broadcasts. However, the transmission of digital broadcast in MPEG-2 format is being explored and occurring as an alternative. In this manner, the user would have a tuner capable of receiving the direct terrestrial link information containing the television or radio signals. Once demodulated, the transport stream information could be provided to a desktop unit, or decoder, owned by the end user.
Service provider broadcast would include broadcast to the home provided by cable television providers, telephone company providers, or other independent providers. In this configuration, the service provider first receives the number of signals which can be ultimately provided to the end user. Examples of such received signals include satellite feeds, terrestrial feeds, switched video sources, local video sources such as tapes, or laser disk DVD""s, as well as traditional table feeds. Based upon the end users demands, the received information can be selectively provided to the end user.
In one manner, the selected feed by the service provider can be provided directly to an end user through a twisted pair connection, which may include a high speed digital subscriber link (DSL) capable of providing data at higher rates than traditionally associated with plain old telephone system (POTS) connections.
In another implementation, the service provider would provide information from a central office or a head-end to a fiber node. A specific fiber node is generally used to support more than one end user. Examples of the use of such fiber nodes includes a fiber coaxial bus (FCB) whereby a fiber link provides the signal containing a large amount of data to a fiber node which in turn drives coaxial cable having a taps. A decoding device attached to taps at user side can receive the appropriate broadcasting signal.
Another example of a fiber node is bi-directional fiber coaxial bus. While similar to the FCB bus, the bidirectional FCB bus is also capable of transmitting data back to the central office or the head-end as well as receiving it. Yet another fiber node example is a hybrid fiber coax, which uses coaxial cable and branch topology toward network interface units. Yet another example associated with service providers is known as fiber to the curb, whereby digital signaling is carried from the central office to the optical network unit which serves only a few dozen homes. Locally, a hybrid twisted pair coaxial pairs will connect to the optical network unit with the consumer""s decoder. Twist repair cable carries digital video in the 5 to 40 megahertz range to no more than 500 feet from the fiber connection. Therefore, the number of homes capable of being served by a single optical network unit is limited. Analog television signals are carried in a coaxial cable from the fiber node.
One problem associated with the flexibility of the MPEG-2 standard is that once the transport stream is received, demodulated, and decrypted, the resulting data stream can still have a variety of variations which need be known before the data stream can be properly utilized. For example, the MPEG-2 specification does not indicate a specific set of control signals to be provided with the transport stream, how received data and control signals are qualified, nor the precise format of the actual data transmitted. As a result, implementations of set top boxes require specific service provider information. Specific service provider information results in an incompatibility among transport streams schemes provided by different service providers or cable operators. As a result, chip sets are designed and dedicated to support specific service provider""s set top boxes.
Prior art FIG. 4 illustrates a prior art system for parsing a transport stream. The transport parser of the prior art would receive individual packets from the framer. Based upon the PID value, the transport parser would store the TSP data to be used by the system or the graphics engine in a local buffer.
When the transport parser""s local buffer was filled, the transport parser would cause a bus request to the appropriate controller (system or video) to initialize a transfer of at least some of the buffered data.
However, when the prior art host video or graphics system needed more data from the transport parser prior to the transport parser initializing the transfer, the system would initialize the transfer by generating a request to access data in the transport parser buffer. Since the bus used internally by the transport parser buffer may have other clients, the host system may have to wait to access the bus. The overall performance of the host system is reduced as a result of the system waiting on data.
Therefore, a system and method of receiving transport stream information that allows for more flexibility and improved performance in terms of data handling, data parsing, design implementation, data stream acquisition would be advantageous.